Coupler
A coupler, or coupling, is a device for joining rail vehicles in a train. This is a major part on a locomotive, wagon, or multiple unit, third in importance after power-source and gauge. A coupler is part of larger draft gear assembly, that may include links, drawhooks, drawbars, yokes, etc. Manual, Semi-Automatic, and Automatic Couplers There are 3 very general types of couplers used on railways worldwide: * Manual Couplers with manual only mechanical, pneumatic, and electric connections. * Semi-Automatic Couplers with automatic mechanical connection, but manual only pneumatic and electric connections. * Automatic Couplers with fully automatic mechanical, pneumatic, and electric connections. Pin-and-link Couplers This archaic design, sometimes called pin-coupler, dates back to the very early days of steam traction. Today, this design is only used on historical narrow gauge railways. Operation is simple; a drawbar projecting away from the frame allows access to a vertical pin that holds a link in place. The link extends out the end of the drawbar. As two railcars come together, the opposite pin is raised, the link is placed inside the opposite drawbar, then the pin is lowered, thus joining the cars. Uncoupling was accomplished by performing the same procedure in reverse. Although this coupler was very simple in its design and inexpensive, it was also very dangerous; This type of coupler caused many injuries and deaths, and the respective links and pins were often stolen, rendering the coupler useless. This type of coupler was outlawed and ordered replaced after 1900 in the United States, and was superseded by the Janney or AAR coupler. Three-link Couplers The old three-link coupler has only recently started to be replaced on UK rolling stock. Preferred by railways for its simplicity and low cost, today it is typically used only on freight stock. Vehicles fitted with this design have drawhooks that connect to drawbars internally. Each drawhook has a permanent three-link coupler hanging vertically from the hook's base, and only one is used when joining occurs; when one coupler is lifted over the adjacent vehicle's drawhook. This system is flexible in the fact that a shunting pole can be used to lift the link over the drawhook, which is safer than being between the buffers. However, the downside to this system is that it is loosely coupled meaning that the considerable slack is taken up as the locomotive sets off — in other words the train sets off one car at a time — and when the locomotive stops there is a concertina effect whereby all the cars stop one after the other. This causes wear and tear on the rolling stock, especially brakes and buffers, thus only slow freight trains could be equipped with three-link couplers. An upside is less of the train's weight is on the locomotive while its starting up the train; a reason why it survived for so long. The type is compatible and interchangeable with screw couplers. Instanter Couplers The instanter coupler was an improvement over the three-link coupler. Its basic design was similar, but the two links that were held by the drawhooks were themselves joined by a pear-shaped object with notches in its design. These notches allowed for two states: an open state and a closed state. A shunting pole was used to switch it between states; the open state kept cars joined but allowed uncoupling, while the closed state held cars together while running. Screw Couplers The most common type used in Western Europe and the UK, it was a development of the three-link coupler. In essence this is a three-link coupler with a threaded rod replacing the center link. A small slide-handle was used to pull the cars together or push them apart for coupling or uncoupling respectively. This was quite a tricky task as it was hard and fiddly to achieve the operation, and it certainly could not be done via use of a shunting pole. This design was used on passenger fleets, or fast freight trains. This type is compatible and interchangeable with three-link couplers. Janney Couplers Janney\AAR couplers, also known as MCB or ARA couplers, are a SemiAuto design with hinged nuckles; at least one nuckle must be open to allow mating; as coupling occurs, any open nuckle is pushed closed by the palm of the opposing coupler body and a pin auto locks the nuckles closed. To decouple, the cars are pushed together for slack, the lock\pin is raised with a side lever to open one nuckle and the cars are pulled apart. Janney\AAR couplers operate simularly to Willison\CA3 couplers, though with hinged nuckles instead of simpler interlocking heads. An advantage compared to Willison\CA3 couplers is Janney\AAR nuckles intentionally have lower tensile strength than the coupler body\shank, act as "shear pins" when overstressed, and can be replaced onsite by the train crew; a disadvantage is Willison\CA3 couplers mate without concern for nuckle closed\open position. Mandated by Congress in 1893, Janney couplers became standard in NorthAmerica, replacing dangerous Link&Pin couplers and impractical MillerHookPlatform couplers; this greatly reduced injuries and allowed efficient interchange of rollingstock between railroads. Outside NorthAmerica, the Janney coupler was slow to be adopted, due to being incompatible with local railway standards and politics. In Britain and Europe, Janney couplers are used on some unitized freight and passenger stock, known as Alliance\BuckEye\DropHead\SwingHead\Henricot couplers; DropHead and SwingHead couplers pivot to reveal a British\Euro standard Chain coupler. After a long conversion from the chaos of colonial designs, Janney couplers have become a standard on freight stock and passenger coaches in Australia+China+India+Indonesia+Japan+Korea+NewZeaLand+Saudi+SouthAfrica+... Janney\AAR TypeE couplers, superceding ARA TypeD + MCB TypeC, have become a standard on general Freight wagons: BoxCars+CenterBeams+ClosedHoppers+Flats+Gondolas+InterModals+AutoRacks+Reefers+... This version is compatible with other AAR couplers. Janney\AAR TypeF couplers, also known as InterLocks, have become a standard on Locomotives and Freight Gondola\Hopper Rotary + HazMat\Chemical Tank wagons. This version is compatible with other AAR couplers, prevents decoupling\telescoping\punctures during a derailment, minimizes slack, and allows RotaryDumping. Janney\AAR TypeH couplers, also known as TightLocks, have become a standard on Passenger wagons and MultipleUnits. This version is compatible with other AAR couplers, prevents decoupling\telescoping during a derailment, minimizes slack, and allows optional FullAuto Pneumatic\Pipe and Electric\Wire coupling. Willison Couplers Originally designed in 1913 by J.Willison@NationalCastingsCo of Ohio for abusive environments, the rugid SemiAuto Willison coupler (in Full, 3/4, and 1/2 sizes) is a worldwide standard for narrowgauge industrial, mine, and plantation railways. Enlarged and improved by Russia in the 1930s, the Willison\CA3 was made standard for the entire RZD broadgauge railway; this version has cast letters CA3 meaning CоветскихAвто3 in Russian or SA3 meaning SovietAuto3 in English; its used across the Russian subcontinent (Russia, FinLand, Mongolia, Ukraine, Turkey, Iran...). A newer CAKv version (CоветскихAвтоKuppling5) is used in Russ~Euro interchange, being compatible with both Russian\RZD CA3 couplers and Euro\UIC chain couplers. Willison\CA3 couplers operate simularly to Janney\AAR couplers, though with simpler interlocking heads instead of hinged nuckles. An advantage compared to Janney\AAR couplers is Willison\CA3 couplers mate without concern for nuckle closed\open position; a disadvantage is Willison\CA3 couplers do not have breakaway\replaceable nuckles and head\shank failures are not repairable by the train crew. Scharfenberg Couplers This coupler is fully automatic, including pneumatic and electric connections. Developed in the 1930s, it is the most common fully automatic coupler for unit passenger trains worldwide. As the couplers come together, a spring releases the brake pipe cocks, and a rotating cover reveals contacts for electric connections. To uncouple, a pneumatically operated release is activated from the cab. A variant of the Scharfenberg coupler, the Shibata coupler, is the standard coupler used on passenger trains in Japan and Korea; the coupler was developed by Japanese Government Railways engineer Mamoru Shibata who gave the coupler its name. References * RailCarCouplers At OBTS Wiki * RailCarCouplers At WikiPedia * Book: The Railway Data File. Published 2000 by Silverdale Books Category:Locomotive Parts Category:Steam Locomotive Principles Category:Diesel Locomotive Principles Category:Electric Train Principles Category:Encyclopedic articles